To make things easier I'll presume your setup is very simple...
The DNS server in the screenshot will be your internal DNS - this is different to your external and external clients won't resolve 192.168.0.0/24 because that is designated a private subnet - not routable over the public internet.
You will need to configure your external DNS servers to point to 22.214.171.124 instead of 192.168.0.101 and 192.168.0.100.
Then on your firewall port forward all the services you want to provice to the public e.g.
25 for MAIL
80 for HTTP
443 for HTTPS
This will get you your desired result.
ok so to start at the beginning you have a domain ... mydomain.com
You need to make sure it resolves correctly on both the public internet and your network.
In your scenario the easiest thing to do is running a public and private DNS for your setup.
I.e. on your public DNS provider e.g. godaddy/123-reg/uk2 (or whatever it is), point the host A record and the wild card subdomain to 126.96.36.199 this will make sure everything resolves to that IP.
This will make sure every external client knows who mydomain.com is. Then just open the ports on the firewall and forward them to the right server.
I presume you want to be able to access the sites internally too - Configure your local / private DNS server with a new forward lookup zone with mydomain.com and configure it with 192.168.0.100 and .101
This will make sure internal clients can resolve the correct internal address otherwise it will only resolve the public IP and your internal clients won't know where to send the traffic. (unless of course you NAT them on the router although I'm guessing that's out of yours skillset for the time being).